Well we have yet to see any XP1000 really race yet. But knowing the rules are the same for the 900 & 1000 I don't know if there will be a big advantage. Each model has to have its share of mods to be race worthy. The rules say 1000cc max, so you can bore the 900 to 1000cc as many have already done. So HP is not the issue.
It's only a matter of time before we see a competitive 1000, but I don't think they will dominate and obsolete the XP900. Especially a currently competitive XP900. I will say I have not looked at the 1000 close enough with a race prospective to see how it might compare. I will say I have done so with the XP4 900 and I see allot of things that can be done to the XP 900 to make it even better, that I have yet to see anyone do. Many dont seem to be taking advantage of the rules.